WIRING METHODS IN HAZARDOUS LOCATIONS

The NEC^R recommends that wherever possible electrical equipment supplying hazardous locations be installed in less hazardous areas. It also suggests that by adequate ventilation, the hazardous condition may be reduced or eliminated. The installation of dust-collecting systems may greatly reduce the hazards in a Class II location.

Equipment and Fittings

When you are installing or repairing equipment in hazardous locations, first be sure you know exactly how the location is classified. Always select equipment that is specifically designed for that classification. Table 3-8 indicates some of the equipment that should be used in hazardous locations. The table does not include all electrical equipment; nor does it cover specific applications within each class of hazardous location.

As you can see by reviewing table 3-8, Class I locations are considered the most hazardous locations. Rigid metal conduit, intermediate metal conduit (IMC), or type MI (mineral-insulated) cable must be used in most locations. All fixtures and fillings must be explosion proof and threaded.

Sealing and Bonding

The NEC^R requires that seals be installed in conduit systems in a majority of Class I, Division 1 and 2 locations. The purpose of the seal is to prevent an explosion in an enclosure from traveling through the conduit to other enclosures. Seals are required in conduits as follows:

1. In each conduit run entering an enclosure where sparks, arcs, or high temperature could be present. Seals must be placed as close as practicable but not more than 18 inches from the enclosure.

2. In each conduit run of 2-inch size or larger entering an enclosure that houses terminals, splices, or taps.

3. In each conduit run passing from a Class I hazardous location into a nonhazardous location. The seal may be installed at any convenient point in the run on either side of the boundary.

If there is a possibility that liquid or other condensed vapor may build up in an enclosure or conduit run, a drainage system has to be installed to prevent accumulation in the system.

Grounding

Grounding requirements in hazardous locations are more stringent than in nonhazardous areas. The use of double locknuts or locknut and bushing grounding methods is not allowed in hazardous locations. Bonding jumpers with approved fittings must be installed to assure grounding continuity in Class I, II, and III locations.

Table 3-8.\Equipment Requirements in Hazardous Locations

NOTE: MI CABLE IS APPROVED FOR ALL HAZARDOUS LOCATIONS. 3-15